Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infection in infants and young children, however no vaccine is currently available. The overall objective of this grant is to develop optimal live attenuated RSV vaccine candidate(s). The significance of this P01 is that it brings together a multidisciplinary group of investigators to leverage a novel observation that infants with severe RSV disease display a pattern of inadequate (or suppressed) immune responses. The grant will simultaneously attack this problem on multiple fronts by developing a vaccine with increased immunogenicity, attenuating the virus in a novel, `tunable' way, improving its yield in cell culture to improve vaccine production, and using gene expression and new antibody detection tools for analysis of the immune response in order to predict vaccine effectiveness and safety. These candidates will be tested first in vitro in primary well differentiated human airway epithelial cultures. Vaccine candidates with the desired characteristics will be selected for testing in vivo in cotton rats for their attenuation and their ability to induce a `safe' host response (similar to natural mild RSV disease in infants), and potent neutralizing antibodies to RSV. Combination mutants will be recycled through this system, resulting in the selection of one optimal vaccine candidate and rank order of excellent backups. By integrating the host response to RSV infection with modifications of the virus that improve these responses, the four projects of this P01 will synergize to develop an optimized live attenuated RSV vaccine candidate ready for testing in human primates and possibly clinical trials.
Respiratory syncytial virus (RSV) is the most frequent cause of lower respiratory tract infection in infants and young children and is responsible for a large number of hospitalizations and mortality worldwide. Indeed, recent data indicates that RSV is the second most frequent cause of death (after malaria) during the first year of life. Despite decades of work we still do not have an effective vaccine to protect children against this infection, like the two excellent vaccines that protect against measles and mumps, two similar viruses. This project will solve the three major problems that have delayed the development an effective attenuated vaccine against this virus: 1) RSV suppresses interferon a critical molecule for the initiation of the body's immune response against the virus, thereby preventing the development of protective immunity against this viral infection; 2) the cells used to grow RSV (to prepare vaccines for studies) inactivates one important protein of the virus and makes the production of the virus very inefficient and expensive; and 3) the process used to make the virus less likely to cause symptoms (attenuation) may not be ideal. We have developed solutions to solve all these three problems. In addition, we have developed a new method to select the best vaccine candidates by adopting into the animal model information on the protective immune responses measured in children with RSV infection. In this way, we will optimize the development of new vaccines to prevent RSV infections more efficiently. Project 1: Enhance Immunogenicity of RSV Vaccines by Altering NS1 Function Project Leader (PL): Teng, M. DESCRIPTION (as provided by applicant): One of the stumbling blocks to development of a live-attenuated RSV vaccine is induction of long-lasting immunity, which does not occur even with wild-type RSV infection. Since induction of robust adaptive immunity responses requires a strong innate immune activation, the short-lived anti-RSV response may be due to viral inhibition of type I interferon (IFN) induction. Antagonism of IFN production is largely due to the RSV NS1 protein, which is not absolutely essential for virus replication in culture although deletion of NS1 results in decreased viral replication even in IFN-deficient cells such as Vero. This proposal will identify domains and/or specific residues of NS1 responsible for IFN antagonism by targeted mutagenesis. Mutants that ablate the IFN antagonist function without affecting protein stability will be inserted into recombinant RSV (rRSV) and tested for their capacity to replicate in Vero cells and induce IFN in A549 cells. NS1 mutant rRSV that induce high levels of IFN expression and replicate well in these cell lines will be tested for IFN antagonism and replication in human airway epithelial (HAE) cultures. Further, the NS1 mutant rRSV will be tested in cotton rats, which are the best small animal model for RSV infection to determine replication in vivo, pathogenicity, immunogenicity, and protection from WT challenge. The best candidate NS1 mutants will be combined with the `repaired' G gene (Project 2) and the best attenuating L methyltransferase (MTase) mutations (Project 3) to produce double and triple mutant viruses that replicate well in Vero cells, induce high levels of IFN, efficiently infect HAE culture, and are attenuated and protective in cotton rats. Although beyond the scope of this P01, these vaccine candidates will be tested in non-human primate trials in the future.
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